Impact of LET on biological response to Flash irradiations
Recent studies with electron and proton beams have shown that irradiation at dose rates above 40 Gy/s can be as effective in inhibiting tumor growth as irradiation at the conventional dose currently used (typically 1 Gy/min) but much less toxic to healthy tissues. This phenomenon is known as the “FLASH effect”. This effect is considered one of the most important discoveries in the recent history of radiobiology due to its potential to improve the therapeutic window between tumor control and normal tissue toxicity. Recent studies show that the biological mechanisms of the FLASH effect are linked to differential tissue oxygenation. However, the exact mechanisms of the cellular biological effects of FLASH irradiations are not completely clear and some are even contradictory.
The objective of this project is a molecular characterization of the FLASH effect on a model system perfectly controlled in vitro. FLASH irradiations of cancer cells and healthy cells will be compared to conventional dose rate irradiations using electrons and carbon ions in the two associated laboratories. The differential effect will be related to the oxygenation condition of the cells, REDOX/mitochondrial metabolism and general changes in cellular metabolism.
Study of plastic scintillators for passive and active neutron measurements
The proposed doctoral work is dedicated to optimizing non-destructive characterization methods for the quantity of plutonium in radioactive waste packages. One of the primary nuclear measurement methods to achieve this goal is based on the passive counting of coincidences between spontaneously fissioned neutrons. Most neutron measurement stations are equipped with 3He counters, which have the advantage of good detection efficiency while being less influenced by gamma radiation.
However, the price of these detectors has significantly increased in recent years, and they are relatively slow as they require prior thermalization of the neutrons to be detected. Plastic scintillators offer a 5 to 10 times less expensive alternative with equivalent detection efficiency, making them attractive for implementation in industrial stations. In exchange, they are highly sensitive to gamma radiation and the phenomenon of crosstalk (parasitic coincidences due to interactions between neighboring detectors). An innovative method for discriminating between useful and parasitic coincidences by differentiating the time of flight between neutrons and gamma radiation has been developed and validated in previous work.
There are still significant practical challenges addressed by this thesis in order to move towards an industrial neutron measurement station equipped with these scintillators, particularly for technological waste (ORANO La Hague, MELOX Cadarache). The primary objective in passive neutron measurement will be to advance in detection efficiency, data processing, and reducing uncertainties related to matrix effects and nuclear material localization, closely integrating experiments and modeling. A secondary objective of the thesis will be to demonstrate the feasibility of active neutron measurement in terms of data processing and resilience to high counting rates for quantifying the mass of nuclear material (detection of neutrons induced by a neutron generator).
The proposed doctoral work is dedicated to optimizing non-destructive characterization methods for the quantity of plutonium in radioactive waste packages. One of the primary nuclear measurement methods to achieve this goal is based on the passive counting of coincidences between spontaneously fissioned neutrons. Most neutron measurement stations are equipped with 3He counters, which have the advantage of good detection efficiency while being less influenced by gamma radiation.
However, the price of these detectors has significantly increased in recent years, and they are relatively slow as they require prior thermalization of the neutrons to be detected. Plastic scintillators offer a 5 to 10 times less expensive alternative with equivalent detection efficiency, making them attractive for implementation in industrial stations. In exchange, they are highly sensitive to gamma radiation and the phenomenon of crosstalk (parasitic coincidences due to interactions between neighboring detectors). An innovative method for discriminating between useful and parasitic coincidences by differentiating the time of flight between neutrons and gamma radiation has been developed and validated in previous work.
There are still significant practical challenges addressed by this thesis in order to move towards an industrial neutron measurement station equipped with these scintillators, particularly for technological waste (ORANO La Hague, MELOX Cadarache). The primary objective in passive neutron measurement will be to advance in detection efficiency, data processing, and reducing uncertainties related to matrix effects and nuclear material localization, closely integrating experiments and modeling. A secondary objective of the thesis will be to demonstrate the feasibility of active neutron measurement in terms of data processing and resilience to high counting rates for quantifying the mass of nuclear material (detection of neutrons induced by a neutron generator).
This work opens up career prospects particularly in research centers and R&D departments in industry.
A master internship is proposed by the team in addition to the thesis.
Imaging with Micromegas detectors with Optical readout
Recent developments have shown that coupling a Micromegas gaseous detector on a glass substrate with a transparent anode and a CCD camera enable the optical readout of Micromegas detectors with an impressive spatial resolution showing that the glass Micromegas detector is well-suited for imaging. This feasibility test has been effectuated with low-X-ray photons permitting energy resolved imaging. This test opens the way to different applications. Here we will focus, on one hand, on neutron imaging for non-destructive examination of highly gamma-ray emitting objects, such as fresh irradiated nuclear fuel or radioactive waste and on the other hand, we would like to develop a beta imager at the cell level in the field of anticancerous drug studies.
Both applications require gas simulations to optimize light yields, optimization of the camera operation mode and design of the detectors in view of the specific constraints of reactor dismantling and medical applications: spatial resolution and strong gamma suppression for neutron imaging and precise rate and energy spectrum measurements for the beta. The image acquisition will be optimized for each case and dedicated processing algorithms will be developed.